Why were there protests?

Mr Putin was re-elected president with more than 76% of the vote, his best ever election performance, but widespread irregularities were reported by some international observers. Allegations of ballot-rigging had dogged previous elections too.

The country's best-known opposition leader, Alexei Navalny, was barred from standing against Mr Putin, on grounds of a conviction for embezzlement which he denies and alleges was politically motivated.

Mr Navalny was arrested briefly as he tried to join Saturday's unauthorised protest rally in Moscow under the slogan "He's not our tsar".

Domestic opponents accuse Mr Putin of undermining democracy in Russia - a policy dubbed "managed democracy" - to keep genuine opposition parties out of parliament and ensure that he and his allies retain power indefinitely.

Could Putin just go on and on?

First elected president in 2000, Mr Putin renewed his four-year term in 2004 before stepping aside in 2008 to serve as prime minister under his protege, Dmitry Medvedev, because by law he could serve only two consecutive terms.

Few doubted who was really in charge and in 2012 Mr Putin returned as president, this time for a term of six years.

When he reaches the end of his fourth term in 2024, he will have been in power for nearly a quarter of a century.

That would still fall short of Soviet dictator Joseph Stalin's 31 years in power or, indeed, the reigns of some Russian tsars such as Alexander II (26 years) and Nicholas I (30 years).